Let the number of toys produced on that day be x.
Therefore, the cost of production (in rupees) of each toy that day = 55 – x
So, the total cost of production (in rupees) that day = x (55 – x)
Therefore, x (55 – x) = 750
i.e., 55x – x2 = 750
i.e., – x2 + 55x – 750 = 0
i.e., x2 – 55x + 750 = 0
Therefore, the number of toys produced that day satisfies the quadratic equation
x2 – 55x + 750 = 0
which is the required representation of the problem mathematically.